Production of high-purity polycrystalline silicon rod for semiconductor applications

ABSTRACT

Disclosed are .[.a.]. processes and reactors for rapidly producing large diameter, high-purity polycrystalline silicon rods for semiconductor applications by the deposition of silicon from a gas containing a silane compound. The equipment includes a reactor vessel which encloses a powder catcher having a cooled surface. Also within the vessel is a cylindrical water jacket which defines multiple reaction chambers. The silicon powder generated in this process adheres to the coolest surfaces, which are those of the powder catcher, and is thereby collected. Little of the powder adheres to the walls of the reaction chambers. In some embodiments, a fan can be provided to increase gas circulation.

This is a continuation of application Ser. No. 296,964, filed Aug. 26,1994, .Iadd.now U.S. Pat. No. 5,478,396, .Iaddend.which is acontinuation-in-part of application Ser. No. 953,480, filed Sep. 28,1992, now U.S. Pat. No. 5,382,419.

BACKGROUND OF THE INVENTION

The present invention relates to a process and equipment for theproduction of high-purity polycrystalline silicon in rod form forsemiconductor applications. The polycrystalline silicon is used as theraw material in the fabrication of single crystal silicon forsemiconductors by the CZ (Czochralski) method or the FZ (float zone)method.

The most common method of producing polycrystalline silicon, which is araw material used for the production of single crystal silicon forsemiconductors, has been to deposit silicon on starter filaments bythermal decomposition of a halosilane compound, such as trichlorosilane,so as to produce large-diameter silicon rods. Japanese Patent Laid-OpenNo. 56-105622 discloses a reactor structure using a chloride-type silanein which a large number of electrodes are arranged on a circular plateand a large number of silicon starter filaments are arranged in areverse-U-shaped or a square-reverse-U-shaped form.

This technique, however, is not suitable for industrial scale productionof polycrystalline silicon from a silane compound, such as monosilanegas or disilane gas, which is not halogenated. At a temperature ofseveral hundred degrees or more, monosilane gas decomposes and therebygenerates a fine silicon powder. The presence of such powder causes anumber of difficulties and, in particular, can seriously hinder thegrowth of silicon rods. Further, where the high-temperature silicon rodsface each other, surface irregularities are generated, therebydeteriorating product quality.

A known technique for dealing with the above problems is disclosed inU.S. Pat. No. 4,150,168, according to which red-hot silicon starterfilaments are thermally insulated from each other so as to preventvapor-phase temperature rise and as to eliminate thermal influences fromthe adjacent heated silicon rods, thereby obtaining uniform siliconrods.

However, in the industrial scale production of silicon rods by thermaldecomposition of monosilane, it is impossible, even with theabove-mentioned technique, to reduce the silicon powder generation tozero. The generated silicon powder is deposited on the reactor walls.When it has accumulated to a thickness of several mm, the silicon powderspontaneously separates from the walls and falls, part of the fallingpowder contacting and adhering to the growing silicon rods. The portionof the powder which adheres to the silicon rods may lead to powderintrusion, abnormal dendrite growth or the like, resulting in defectiveproducts.

Japanese Patent Laid-Open No. 61-101410 discloses a technique which issomewhat improved over that of U.S. Pat. No. 4,150,168, in that thereactor has a different heat insulation structure. However, for reasonsgiven in a reference by Hogness et al. (Hogness, T. R., Wilson, T. L.,Johnson, W. C.: "The Thermal Decomposition of Silane" J. Am. Chem. Soc.58: 108-112, 1936), the new technique is likely to require a seriousdecrease in reaction speed in order to obtain the restraint of thesilicon powder growth.

Japanese Patent Publication No. 44-31717 discloses a technique forcollecting silicon powder outside a reactor. With this technique, thesilicon powder generated in the course of production of polycrystallinesilicon rods is taken out of the reactor along with the partially spentreactant gas. The powder is collected by means of a filter, and the gascleared of powder is re-circulated through the reactor. A similartechnique is disclosed in U.S. Pat. No. 4,831,964. A problem with thesetechniques is that they require large scale equipment external to thereactor. Thus, they involve an increase in the number of components,resulting in an increase in the opportunity of contamination. Further,the silicon powder adhering to such components accumulates in placeswhere it cannot be easily removed by cleaning or in places which arehard to clean. The silicon powder is very active, so that it is easilyignited by static electricity or the like. And, an ignition of a mixtureof air and silicon powder can cause a detonation. It is another problemthat silicon powder deteriorates the sealing property of valves used toisolate the reactor from the external equipment when extracting siliconrods, performing cleaning, etc. Thus, handling of the silicon powder isbest kept to a minimum.

Japanese Patent Publication No. 52-36490 discloses a special method ofcausing a reactive gas to circulate in a reactor. The method employs ameans for uniformalizing the concentration of monosilane gas in thereactor. It prevents monosilane gas at high concentration or puremonosilane gas from reaching a high-temperature section of the reactorin the vicinity of the silicon starter filaments, thereby restrainingthe generation of silicon powder. A problem with this method is that nomeasure is taken to contain the radiation of heat from the heatgenerating elements. Thus, the technique is not suitable for the thermaldecomposition of monosilane gas. Further, because the rods are not grownin separate reaction chambers, it is difficult to supply the reactivegas in a uniform fashion. As a result, it is hard for the grown siliconrods to attain a high level of roundness in cross section, the roddiameter differing from rod to rod.

A technique for increasing the flow velocity of reactive gas isdisclosed in Japanese Patent Laid-Open No. 63-123806, according to whichan agitator is provided in the top or bottom section of a reactor. Thistechnique, however, is not suitable where a nonhalogenated silanecompound gas is used since silicon powder would be generated anddispersed by the agitator.

Apart from the problems discussed above, these prior techniques have aproblem which is common to them: the absence of a means for preventingthe silicon powder which is generated by vapor-phase homogeneousreaction, from accumulating on the walls around the silicon rods and onthe reactor ceiling. Defective products result due to the adhesion ofsilicon powder detached from the reactor walls. Silicon rods are hard todissolve where the silicon powder has adhered, thus makingmonocrystallization difficult. Therefore, silicon rods with adheredpowder are suitable for neither the CZ or the FZ method.

Further, it is considered that the precipitation rate of polycrystallinesilicon will be low when a reactor structure encourages the accumulationof silicon powder on the walls around growing polycrystalline siliconrods and on walls in the reactor ceiling section.

Polycrystalline silicon, in the form of rods or chunks obtained bycrushing rods, is being widely used in the production of single crystalsilicon by the CZ or FZ method. A high purity level and competitive costare particularly required of polycrystalline silicon rods forsemiconductor applications. These requirements are becoming severer fromyear to year. The present invention has been made in view of the aboveproblems in the prior art.

Accordingly, there is a need to provide a process and equipment whichmake it possible to produce large diameter polycrystalline silicon rodsrapidly while making efficient use of a gas feedstock that contains anonhalogenated silane compound.

SUMMARY OF THE INVENTION

The present invention provides a process and equipment for theproduction of polycrystalline silicon in rod form for semiconductorapplications by thermal decomposition of a highly refined reactant gascontaining a nonhalogenated silane compound such as monosilane ordisilane.

Walls inside a reactor define multiple reaction chambers for growingpolycrystalline silicon in rod form and provide powder catchers forcollecting silicon powder generated during the thermal decomposition ofthe silane compound. The powder catcher walls define at least one powdercatcher chamber that is separate from, but communicates with, thereaction chambers. Both the reaction and powder catcher chambers defineflow paths for the reactant gas.

In a first embodiment, the reactor contains a plurality of powdercatchers consisting of vertically-extending cylindrical water jacketswhich are arranged concentrically, and multiple reaction chambers whichare cylindrical channels defined by an outer cylindrical water jacketsurrounding the powder catchers. The powder catcher chambers andreaction chambers communicate via spaces defined above and below theouter water jacket.

Preferably, the total cross-sectional area of the powder catcherchambers is larger than that of the reaction chambers, .[.and-the.]..Iadd.and the .Iaddend.total surface area of the powder catcher walls islarger than that of the walls which define the reaction chambers.Resistant baffle plates are provided at the lower ends of the reactionchambers and at the upper or the lower ends of the powder catcherchambers for the purpose of controlling reactant gas flow; a metal orceramic plate is installed as a heat shield plate in the top section ofthe reactor; and a plurality of nozzles for feeding monosilane gas intothe reactor are positioned within the upper regions of the powdercatcher chambers and directed circumferentially with respect to thepowder catchers.

Further, in a method of producing polycrystalline silicon using theabove-described equipment for the production of polycrystalline siliconin rod form for semiconductor applications, the relationshipT2.[.≦.]..Iadd.<.Iaddend.T1.[.≦.]..Iadd.<.Iaddend.T3 is maintained,where T1 is the wall temperature of the reaction chambers, T2 is thewall temperature of the powder catchers, and T3 is the wall temperatureof the reactor ceiling. For optimum results, temperature control iseffected in such a way that T1 is .[.b.]. 25° C. or more, T2 is 25° C.or less, and T3 is 70° C. or more.

In other embodiments, the powder catcher is located at an elevationabove the reaction chambers. The powder catcher, which mostadvantageously includes an array of heat exchange tubes, is preferablyoffset horizontally so that the tubes are not located directly above thereaction chambers. The tubes are positioned such that gas flowing fromthe reaction chambers flows through the array of tubes where powderdeposits on the cooled surface provided by the tubes. At least a portionof the reactant gas that passes through the tubes is recirculated intothe reaction chambers.

.[.In-either.]. .Iadd.In either .Iaddend.embodiment, a fan can beinstalled at a position in the reactant gas flow and, more specifically,at a position below the powder catcher(s) so as to control the reactantgas circulation in the reactor on the basis of the rotating speed of thefan. To direct the reactive gas flow to pass through the fan, a shroudcan be provided to isolate the powder catcher chamber(s) and thereaction chambers from each other.

The above-described apparatuses provide one or more of the followingadvantages:

(1) The degree of freedom in setting the reaction conditions issubstantially increased, as compared with the prior art, by virtue of aconstruction in which a large number of reaction chambers for growingpolycrystalline silicon in rod form and one or more powder catchers forcollecting silicon powder are arranged inside a common reactor vessel insuch a way as to extend along a reactant gas flow path and as to beseparate from each other. Since the reaction chambers and the powdercatcher(s) are separated from each other and installed inside the samereactor, optimum conditions can be obtained for their respectivefunctions. That is, by making the cooling temperature of the powdercatcher(s) lower than that of the reaction chambers, the flow velocityof the descending gas is increased, with the result that the ascendingspeed of the gas flow in the reaction chambers is increased, therebymaking it possible to increase the rate of reactant gas supply, producelarge diameter polycrystalline silicon rods in a short time, and reduceproduction costs.

(2) When the wall surfaces of the powder catchers or the gas returnpassageways are vertical and the total space cross-sectional area ofvertical powder catcher chambers or gas return passageways is largerthan that of the reaction chambers, the resistance with respect to thedownward flow of the reactant gas is reduced, thereby increasing theflow velocity of the gas flowing upwards in the reaction chambers.Accordingly, it is possible to feed a larger amount of reactant gas,thereby raising the growth speed of the polycrystalline silicon rods.Further, the adhesion of silicon powder to the reaction chamber wallscan be prevented to a large degree.

(3) By making the total surface area of the powder catchers larger thanthat of the reaction chamber walls, the collection of silicon powder bythe powder catchers is facilitated.

(4) When resistant plates for reactant gas flow control are provided atthe upper ends of the reaction chambers and/or at the upper or the lowerends of vertical powder catcher chambers, it is possible to adjust thesupply of gas to the reaction chambers and thereby obtain apredetermined uniform flow rate where there would otherwise be someirregularity in the gas flow pattern inside the reactor. As a result,the gas flow in the reactor is uniformalized, and the growing conditionsfor the polycrystalline silicon rods can be optimized.

(5) When a shield plate is provided above the reaction chambers, it ispossible to maintain the ceiling section of the reactor vessel at ahigher temperature, thereby more reliably preventing the adhesion ofsilicon powder to the ceiling section of the reactor vessel.

(6) When a plurality of feed nozzles for feeding part of the reactantgas into the reactor are arranged at a level corresponding to the upperregions of vertical powder catcher chambers and in such a way as to bedirected in the circumferential direction with respect to the powdercatchers, new reactant gas can be injected horizontally at an angle of90° with respect to the downstream flow in the powder catcherchamber(s). This agitates the recirculating reactant gas and makes theoverall concentration of silicon compound gas more uniform. Due to thisenhancement in mixing, it is possible to feed a large amount of reactantgas under optimum gas distribution conditions. Accordingly, the growingspeed of the polycrystalline silicon rods is increased.

(7) Since the temperature control can be effected in such a way that thereaction chamber wall temperature T1 is 25° C. or more, thepowder-catcher wall temperature T2 is 25° C. or less, and thereactor-ceiling wall temperature T3 is 70° C. or more, the velocity ofthe monosilane gas, flowing downwards along the powder catcher walls, isincreased, thereby increasing the velocity of the gas flowing upwardsinside the reaction chambers. Due to this arrangement, reactant gas canbe supplied to the reaction chambers at a high rate, thereby making itpossible to produce large-diameter silicon rods in a short period oftime. Further, as a result of the increase in the gas flow velocity, gasdoes not linger in the reaction chambers so that adhesion of siliconpowder to the reaction chamber walls can be avoided. Since thetemperature of the powder catcher walls is set to be lower than that ofthe other surfaces inside the reactor, the silicon powder collectingeffect is enhanced remarkably.

(8) When a fan is provided below the powder catcher(s) and a shroudisolates the powder catcher chambers or gas return passageway(s).[.from-the.]. .Iadd.from the .Iaddend.reaction chambers, the flowvelocity of the gas fed into the reaction chambers can be controlled byadjusting the fan rotating speed and it is possible to further increasethe rate of reactant gas feed through the reaction chambers. Byadjusting the fan velocity, it is possible to achieve the optimum gasflow rate, thereby increasing the growing speed of the polycrystallinerods.

Most reactors in use nowadays are made of metal, taking intoconsideration equipment cost, management, safety, and the like. In theproduction equipment of the present invention, a nonhalogenated silanegas is used instead of a chloride-type silane gas, which is highlycorrosive. Therefore, a secondary contamination of polycrystallinesilicon due to corrosion of the reactor can be avoided. Further, thethermal decomposition of nonhalogenated silane compound gas isaccompanied by a vapor-phase uniform decomposition, which is a reactioninvolving the generation of silicon powder, so that it is remarkablydifferent from the thermal decomposition of a chloride-type silane gas.Therefore, adopting a reactor configuration which is the same as that ofa reactor using a halogenated silane gas, would result in a rather lowreaction speed and yield at a very low level.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Drawings:

FIG. 1 is a schematic vertical sectional view showing a first reactoraccording to the present invention for the production of high-puritypolycrystalline silicon rods for semiconductor applications;

FIG. 2 is a partial perspective view showing an upper portion of acooling jacket and of reaction chambers defined thereby;

FIG. 3 is a partial schematic sectional view taken along line 3--3 ofFIG. 1;

FIG. 4 is a schematic vertical sectional view showing a second reactoraccording to the present invention;

FIG. 5 is a schematic vertical sectional view showing a third reactoraccording to the present invention;

FIG. 6 is a schematic vertical sectional view showing a fourth reactoraccording to the present invention.

DETAILED DESCRIPTION

Preferred embodiments of processes and equipment for the production ofhigh-purity polycrystalline silicon in rod form for semiconductorapplications, according to the present invention, will now be describedwith reference to the drawings.

In the equipment shown in FIGS. 1-3, a verger-type cover or bell 1 and around base plate 2 provide a reactor vessel. A cylindrical partitionmember 4, that is a heat exchanger or water jacket and that is shaped todefine multiple reaction chambers 3, is provided inside a cylindricalspace defined by the cover 1 and base plate 2. Cylindrical powdercatchers 5 and 6 are concentrically arranged within the partition member4. The water jacket 4 and powder catchers 5 and 6 are sized and spacedsuch that there are annular powder catcher chambers therebetween and acylindrical powder catcher chamber at the center of the powder catcher6. The powder catcher chambers serve as gas downflow passageways. Thereaction chambers 3 consist of cylindrical spaces arranged at equalintervals in the vicinity of the outer periphery of the water jacket 4.Openings 4a leading from the outer periphery of the water jacket 4 tothe reaction chambers 3 are provided for purpose of enabling theextraction of polycrystalline silicon rods which have been completelygrown.

The cover 1 and the powder catchers 5 and 6 are at least partiallyhollow and serve as water cooled heat exchangers or cooling jackets. Thecover 1 is formed by connecting upper and lower cover sections 1a and 1bwith each other. The lower surface of the upper cover section 1a servesas the reactor vessel ceiling. Provided in the upper cover section 1aare a cooling water inlet 1c and a cooling water outlet 1d. Provided inthe lower cover section 1b are a cooling water inlet 1e and a coolingwater outlet 1f. As it moves from the inlet 1c to the outlet 1d, coolingwater flows through the space between the inner and outer walls of thecover. Connected to the bottoms of the water jacket 4 and the powdercatchers 5 and 6 are cooling water supply pipes 7a, 7b, 7c and 7d whichextend from below through the base plate 2. The pipes 7b and 7d are usedto supply cooling water to spaces inside the powder catchers 5 and 6 andto discharge it therefrom. Electrodes 9 extend from below through thebase plate 2, through the intermediation of insulating members 8, andare arranged at positions corresponding to the centers of the reactionchambers 3. Chucks 10 are attached to the tips of the electrodes 9. Thewater flowing through the water cooling jackets may be replaced byanother fluid cooling or a heating medium. Further, the powder catchermay be a bundle of pipes or of a coil type.

In the embodiment of FIG. 1, a fan 20 and a shroud 21 are provided belowthe powder catchers 6 to enhance and control the circulation of gasinside the reactor.

A silane gas pipe 11 extends from below through the base plate 2 andupwards between powder catchers 5 and 6. Connected to an annular header12, which is connected to the upper end of the silane gas pipe 11, are aplurality of gas nozzles 13 which are open in the same circumferentialdirection. The nozzles are thus aimed to cause silane gas to movecircumferentially along walls of the powder catchers 5 and 6. Providedinside each of the gas nozzles 13 is a capillary or an orifice to enablethe silane gas to be ejected uniformly through the nozzles 13.

Resistant plates 14 are arranged at appropriate intervals inside thereactor. The plates extend transversely to gas downflow passageways toregulate gas flow. In the illustrated embodiment, the plates 14 arefirmly attached to the upper ends of the powder catchers 5 and 6. Suchresistant plates may also be firmly attached to the lower end of thewater jacket 4 and/or the powder catchers 5 and 6, and/or connected tothe header 12 above the powder catchers 5 and 6. Provided in the spaceabove the water jacket 4 is a heat shield plate 15. An exhaust pipe 16extends through the base plate 2 and can be used to remove spentreactant gas. Silane gas pipes 11a allow silane gas to be evenly ejectedinto each reaction chamber at an arbitrary position 13a on the watercooling jacket 4.

Next, a process for producing polycrystalline silicon rods using theabove apparatus will be described. Silicon starter filaments 17 arepositioned in the reaction chambers 3 and held by the chucks 10. Aboveeach of stepped sections 4b of the water cooling jacket 4, a pair ofsilicon starter filaments 17 are connected to each other at their upperends through a silicon bridge 18. Cooling water is circulated throughthe cover 1, the water jacket 4 and the powder catchers 5 and 6. Thesilicon starter filaments 17 are heated by directly supplyingelectricity thereto through the electrodes 9.

Reactant gas, which contains a silane gas, is fed into the reactorthrough the reactant gas pipes 11, the header 12 and the gas nozzles 13.Reactors according to the present invention are particularly suited foruse with a reactant gas that contains silicon in the form of anonhalogenated silane compound, such as monosilane or disilane, or amixture of such compounds. The reactant gas, which is ejectedhorizontally in the circumferential direction, is agitated by a downwardgas flow along the wall surfaces of the powder catchers 5 and 6. Becausethey are moving in different directions, the gas streams mix and areagitated to produce a combined reactant gas having a uniformconcentration of the silicon-containing compound(s). Then, whileascending inside the reaction chambers 3, which are heated by thesilicon starter filaments 17, the gas reacts to deposit polycrystallinesilicon 19 on the silicon starter filaments 17. Reactant gas which hasbeen blown upwards beyond the reaction chambers 3 next descends alongthe wall surfaces of the powder catchers 5 and 6 and then returns to thereaction chambers 3. It is advantageous to circulate reactant gas at ahigh flow rate so that any silicon powder will remain entrained in thegas until it reaches a cooled surface of the powder catcher. To operateat an increased gas flow rate, the reactant gas can comprise a mixturethat includes one or more nonhalogenated silane compounds and a diluent,such as hydrogen gas or an inert gas such as helium or argon. And,conversely, to achieve a desired rate of silicon deposition on the rods,the rate of gas flow should be increased when the concentration ofsilicon-containing compounds in the reactant gas is reduced. The diluentgas is preferably mixed, using mass flow controllers to maintain adesired ratio, with the silane-containing gas before the reactant gas isinjected into the reactor. However, it would be possible to have aseparate set of injection nozzles (not shown) for injection of thediluent gas.

To inhibit uneven growth in the diameter of the polycrystalline siliconrods at different elevations, a supplementary stream of reactant gas canbe provided through the reactant gas pipe 11a and the gas nozzle 13a.The added gas makes up for the depletion of silane from the reactant gasthat moves upwardly in the reaction chambers 3.

The powder catchers 5 and 6 perform the two functions of collectingsilicon powder and effecting heat exchange. Accordingly, the temperaturein the reaction chambers 3 can be independently regulated to achieve thebest growth conditions for polycrystalline silicon rods.

If the regions surrounding the powder catchers 5 and 6 are cooled to atemperature lower than that of other regions inside the reactor, thevelocity of downward gas flow along the powder catchers 5 and 6 isincreased, with the result that the velocity of the upwards flow in thereaction chambers 3 is increased. As a result, it is possible tocirculate a large volume of silane-containing gas through the reactorchambers 3. Further, since floating silicon powder collects on coolsurfaces, such as on the walls of the powder catchers 5 and 6,accumulation thereof on the walls of the reaction chambers 3 and thereactor ceiling section can be avoided to a large degree.

Because of the multi-layer structure in the horizontal direction of thepowder catchers, it is possible to enhance the cooling effect and thecollection of the silicon powder while suppressing resistance todownward gas flow. However, it is difficult to attach a plurality ofpowder catchers while maintaining a high degree of concentricitythereof. If the gaps between the powder catchers are not uniform, thereactant gas cannot flow uniformly into the different sections of thereactor. To compensate for uneven spacing, the resistant plates orbaffles 14 are attached to the bottom section of the water coolingjacket 4 and to the top or the bottom sections of the powder catchers 5and 6 for the purpose of controlling the gas flow. The width, length andmounting angle of the resistant plates 14 are selected to achieveoptimum results. The resistant plates 14 can also be used to control anyturbulence in the gas flow caused by supports or like structuresattached to the water jacket 4 or the powder catchers 5 and 6 due to anyrequirement in strength.

It is especially important to maintain the relationship:T2.[.≦.]..Iadd.<.Iaddend.T1.[.≦.]..Iadd.<.Iaddend.T3, where T1 is thewall temperature of the reaction chambers 3, T2 is the wall temperatureof the powder catchers 5 and 6, and T3 is the wall temperature of theupper section of the verger-type cover 1. By making the wall temperatureT3 of the reactor ceiling section high, the adhesion of silicon powderto the ceiling section further decreases.

It is desirable that the wall temperature T1 of the reaction chambers 3be 25° C. or more. Further, the temperature of the lower cover section1b opposed to the reaction chambers 3 is also set to be 25° C. or more.A cooling water at a temperature of 30° C. to 40° C. can be easilyobtained by utilizing equipment such as a cooling tower. It is desirablefor the wall temperature T2 of the powder catchers 5 and 6 to be 25° C.or less. Also in this regard, a cooling water at a temperature of 10° C.to 15° C. can be easily achieved by directly utilizing water drawn froma well. Cooling water at a temperature of approximately 5° C. can beeasily supplied by utilizing equipment such as a chiller.

It has been experimentally ascertained that circulating silicon powderis most likely to adhere to and accumulate on surfaces of the lowesttemperature. The lower the temperature, the greater the amount ofadhesion. A cooling water temperature around 5° C. is desirable for thepowder catchers 5 and 6 for powder removal efficiency. It is desirablethat the wall temperature of the reactor ceiling section, i.e., thetemperature T3 of the upper cover section 1a, be 70° C. or more. Whenusing water, the phenomenon of boiling may take place at a mean watertemperature of around 85° C., depending upon the conditions, so that itis more desirable to use a heating medium other than water when atemperature of 85° C. or more is involved. When the difference betweenthe temperatures T1 and T3 becomes approximately 30° C. or more, theeffect of preventing the silicon powder adhesion to the reactor ceilingsection becomes remarkably high.

By installing the heat shield plate 15 above the reaction chambers 3 andkeeping the walls in the region above the reaction chambers 3, to whichsilicon powder should not adhere, at high temperature, little siliconpowder adheres in this region. The heat shield plate 15 may consist of apolished metal plate having high reflectance, for example, a stainlesssteel plate, which excels in heat resistance and corrosion resistance. Aceramic plate excelling in heat resistance, such as a quartz glassplate, may also be used for the heat shield plate 15. The plate 15 maybe annular or a series of separate plates.

While, in the embodiment described above, the reaction chambers 3 areformed as cylindrical spaces having vertical openings through the outerperipheral surface of the water jacket 4, from which the grownpolycrystalline silicon rods are extracted, this should not be construedrestrictively. It is also possible to form the reaction chambers ascompletely cylindrical spaces having no such openings, the grownpolycrystalline silicon rods being extracted by pulling them upwards outof the reaction chambers. Further, it is also possible to providereaction chambers on both the outer and the inner peripheral surfaces ofthe water jacket 4. Or, the water jacket that is equipped with reactionchambers may be provided in a central region of the reactor, with thepowder catchers arranged around it.

When the fan 20 is used, its rotating drive shaft extends through thebase plate 2 and connects to a driving motor (not shown). To prevent theescape of silane gas, which is inclined to ignite spontaneously uponcoming into contact with air, a shaft seal or insulation is provided.Such sealing can be easily realized utilizing known devices such asmagnetic seals. The speed of rotation is selected to provide a gas flowrate which minimizes the deposition of powder at locations from which itcan slough off onto the growing rods. The optimum speed will depend onthe size and shape of the reactor and composition of the circulatinggas. Thus, for any given reactor, the best speed is determined byexperimentation.

In the embodiment of FIG. 4, a verger-type cover or bell 101 and a roundbase plate 102 provide a reactor vessel. A cylindrical partition member103, that is a heat exchanger or water jacket and that is shaped todefine multiple reaction chambers 103, is provided inside a cylindricalspace defined by the cover 101 and base plate 102. A powder catcher 105is positioned at an elevation above the tops of the reaction chambers103. The illustrated powder catcher is a cylindrical array of heatexchange tubes 130 that are concentrically arranged. The array is in theshape of a disk having a central vertical passageway 132. Multiple thinfins (not shown) may be attached to the tubes 130 to increase the areaof the cooled surface that is provided by the powder catcher. Theillustrated powder catcher 105 is positioned so that it is not directlyover the reaction chambers 103. This arrangement reduces the smalllikelihood of agglomerated powder falling from the powder catcher intoone of the reaction chambers. The arrangement is also advantageous inthat an unobstructed region 133 is provided over the reaction chambersso that heated gas is free to rise up and away from the growing rods 119at a rapid rate.

The water jacket 104 and powder catcher 105 are positioned and spacedsuch that gas which exits from the tops of the reaction chambers 103flows through the array of tubes 130 and into the passageway 132. Thepassageway 132, along with a central passageway 134 defined by the waterjacket 104, serves as gas downflow passageway. The reaction chambers 103consist of cylindrical spaces arranged at equal intervals in thevicinity of the outer periphery of the water jacket 104. Openingsleading from the outer periphery of the water jacket 104 to the reactionchambers 103 are provided for purpose of enabling the extraction ofpolycrystalline silicon rods which have been completely grown.

The cover 101 and the tubes 130 of the powder catcher 105 are at leastpartially hollow and serve as water cooled heat exchangers. The cover101 is formed by connecting upper and lower cover sections 101a and 101bwith each other. The lower surface of the upper cover section 101aserves as the reactor vessel ceiling. Provided in the upper coversection 101a are a cooling water inlet 101c and a cooling water outlet101d. Provided in the lower cover section 101b are a cooling water inlet101e and a cooling water outlet 101f. As it moves from the inlet 101c tothe outlet 101d, cooling water flows through the space between the innerand outer walls of the cover. Connected to the bottom of the waterjacket 104 are cooling water supply pipes 107a and 107c which extendfrom below through the base plate 102. Extending through the upper coversection 101a are water supply pipes 107b which provide cooling water tomanifolds 136 for distribution into the tubes 130. Heated water from thetubes 130 is removed via a discharge pipe 107d which also extendsthrough the upper cover section 101a. The water flowing through thewater cooling jacket 104 and tubes 130 may be replaced by another fluidcooling or a heating medium.

Electrodes 109 extend from below through the base plate 102, through theintermediation of insulating members 108, and are arranged at positionscorresponding to the centers of the reaction chambers 103. Chucks 110are attached to the tips of the electrodes 109.

Resistant plates (not shown) can be arranged at appropriate intervalsinside the reactor as explained with regard to the embodiment of FIGS.1-3. The plates extend transversely to gas downflow passageways toregulate gas flow. Provided in the space above the water jacket 4.[.is.]. are heat shield/deflector plates 115. The plates 115 arepositioned so that gas which rises from the reaction chambers 103 ischanneled into the powder catcher 105.

An exhaust pipe 116 extends through the base plate 102 and can be usedto remove spent reactant gas. Reactant gas pipes 111a allow reactant gasto be evenly ejected into each reaction chamber through openings 113a onthe surface of the water cooling jacket 104. To provide an even gasdistribution, the openings are provided at multiple positions and atmultiple elevations. Gas added at the higher elevations makes up for thedepletion of silicon from the reactant gas that moves upwardly in thereaction chambers 103.

Polycrystalline silicon rods are produced .Iadd.by .Iaddend.theapparatus of FIG. 4 by positioning silicon starter filaments 117 are inthe reaction chambers 103 where they are held by the chucks 110. Pairsof silicon starter filaments 117 are connected to each other at theirupper ends through silicon bridges 118. Cooling water is circulatedthrough the cover 101, the water jacket 104 and the powder catcher 105.The silicon starter filaments 117 are heated by directly supplyingelectricity thereto through the electrodes 109. Then, a silicon-bearingreactant gas is fed into the reactor through the reactant gas pipes 111aand the gas nozzles 113a. Then, while ascending inside the reactionchambers 103, which are heated by the silicon starter filaments 117, thegas reacts to deposit polycrystalline silicon 119 on the silicon starterfilaments 117. Reactant gas which has moved upwards beyond the reactionchambers 103, in a laminar convection flow, next passes through the heatexchange tube array and along the wall surfaces of the powder catchertubes 130, descends through the passageways 132 and 134, and thenreturns to the reaction chambers 103. A fan mechanism (not shown) can belocated in or below the passageway 134.

The powder catcher 105 performs the two functions of collecting siliconpowder and effecting heat exchange. Accordingly, the temperature in thereaction chambers 103 can be independently regulated to achieve the bestgrowth conditions for polycrystalline silicon rods. Since floatingsilicon powder collects on cool surfaces, such as on the walls of thepowder catcher tubes 130, accumulation thereof on the walls of thereaction chambers 103 and the reactor ceiling section can be avoided toa large degree.

Another embodiment, as shown in FIG. 5, is closely related to theembodiment of FIG. 4, with like elements being similarly numbered, butincremented by 100 in FIG. 5. In the apparatus of FIG. 5, reactant gasmoves upwardly from the reaction chambers 203 into a tube array of thepowder catcher 205 where the gas is cooled and powder deposits. Thecooled gas is not returned to the bottom of the reactor via a centralpassageway, but instead moves down from the powder catcher and descendsalong the cooled wall 240 of the water jacket 204. A top plate 242 isprovided at the top of the water jacket 204 to direct gas back outwardlyto the region above the reaction chambers 203. An exhaust pipe 216extends through the base plate 202 and top plate 242, for removing spentreactant gas when necessary.

Yet another embodiment is shown in FIG. 6. This embodiment is closelyrelated to the embodiment of FIG. 5, with like elements being similarlynumbered, but incremented by 100 in FIG. 6. In the apparatus of FIG. 5,reactant gas moves upwardly from the reaction chambers 303 into a powdercatcher 305 having two concentric tube arrays. An inner array 350 issimilar to the tube array of FIGS. 4 and 5. An outer tube array 352concentrically surrounds the inner array 350. The outer tube array 352provides an additional surface for the deposit of powder. Mostconveniently the inner and outer arrays are in fluid communication withone another so that a single source of cooled water can feed botharrays. In the illustrated .[.embodiment cooling.]. .Iadd.embodiment,.Iaddend.both a cooling water supply pipe 307b and a cooling waterdischarge pipe 307d enter the reactor through the same opening. And,both .[.pipe.]..Iadd.pipes .Iaddend.are connected to both arrays bymanifolds 356b and 356d .[.respectively. e.]. .Iadd.respectively,.Iaddend.where the gas is cooled and powder deposits.

Having illustrated and described the principles of our invention, itshould be apparent to those persons skilled in the art that such aninvention may be modified in arrangement and detail without departingfrom such principles. For example the powder catcher used in the abovedescribed reactors could be constructed in a variety of configurations,including some combination of cooled tubes, cooled plates, and/or cooledwall surfaces, or the like. We claim as our invention all suchmodifications as come within the true spirit and scope of the followingclaims.

We claim:
 1. A process for the production of polycrystalline siliconrods from a silicon-bearing gas, the process comprising:providing areactor vessel having an interior surface including a floor, a wall anda ceiling, the vessel containing .[.a cooled partition with a wall whichdefines.]. multiple reaction chambers and containing a powder catcherwhich is displaced from the reaction chambers, has a cooled wall, and isin the form of a heat exchange tube array; positioning a starterfilament in each reaction chamber where a polycrystalline silicon rod isto be grown; heating the starter filaments; passing a silicon-bearingreactant gas through the reaction chambers such that polycrystallinesilicon deposits on the starter filaments and forms silicon powder dueto the thermal decomposition of a silicon compound in the reactant gas;and passing the reactant gas, with entrained silicon powder, from thereaction chambers into contact with the cooled wall of the powdercatcher.
 2. The process as defined by claim 1, further comprisingregulating the flow of the reactant gas by positioning a flow resistantplate along the path of reactant gas flowing inside the reactor vessel.3. The process as defined by claim 1, further comprising inhibitingdeposition of silicon powder on the ceiling of the reactor above thereaction chambers by positioning a metal or ceramic heat shield plateabove the reaction chambers such that reactant gas exiting the reactionchambers is diverted from flowing directly to the ceiling of the vessel.4. The process as defined by claim 1, further comprising:providing thepowder catcher in the shape of a cylinder; and injecting the reactantgas alongside and in a circumferential direction with respect to thepowder catcher.
 5. The process as defined by claim 1, further comprisingmaintaining the relationship ofT2.[.≦.]..Iadd.<.Iaddend.T1.[.≦.]..Iadd.<.Iaddend.T3 where T1 is thewall temperature of the reaction chambers, T2 is the wall temperature ofthe powder catcher, and T3 is the reactor ceiling temperature.
 6. Theprocess as defined by claim 5, further comprising maintaining thetemperature to be T1>25° C., T2<25° C., and T3>70° C.
 7. A process forthe production of polycrystalline silicon rods from a silicon-bearinggas, the process comprising:providing a reactor vessel having aninterior surface including a floor, a wall and a ceiling, the vesselcontaining .[.a cooled partition with a wall which defines.]. multiplereaction chambers and containing a powder catcher which is displacedfrom the reaction chambers, has a cooled wall, and is in the shape of adisk that defines a central vertical passageway and that is located atan elevation above the tops of the reaction chambers; positioning astarter filament in each reaction chamber where a polycrystallinesilicon rod is to be grown; heating the starter filaments; passing asilicon-bearing reactant gas through the reaction chambers such thatpolycrystalline silicon deposits on the starter filaments and formssilicon powder due to the thermal decomposition of a silicon compound inthe reactant gas; and passing the reactant gas, with entrained siliconpowder, from the reaction chambers into contact with the cooled wall ofthe powder catcher.
 8. A process for the production of polycrystallinesilicon rods from a silicon-bearing gas, the processcomprising:providing a reactor vessel having an interior surfaceincluding a floor, a wall, and a ceiling, the vessel containing (a) .[.acooled partition with a wall which defines.]. multiple reactionchambers, (b) a powder catcher which is displaced from the reactionchambers, has a cooled wall, and is in the form of a heat exchange tubearray, and (c) a recirculation fan positioned between the powder catcherand the reaction chambers; positioning a starter filament in eachreaction chamber where a polycrystalline silicon rod is to be grown;heating the starter filaments; passing a silicon-bearing reactant gasthrough the reaction chambers such that polycrystalline silicon depositson the starter filaments and forms silicon powder due to the thermaldecomposition of a silane gas in the reactant gas, the silane gas beingselected from the group consisting of monosilane, disilane, and mixturesthereof; passing the reactant gas, with entrained silicon powder, fromthe reaction chambers into contact with the cooled wall of the powdercatcher; and operating the recirculation fan to move reactant gas fromthe vicinity of the powder catcher back into the reaction chambers. 9.The process as defined by claim 8, wherein a metal or ceramic heatshield plate is installed in the top section of the reactor.
 10. Theprocess as defined by claim 8, further comprising channeling allreactant gas in the vicinity of the powder catcher through therecirculation fan.
 11. The process as defined by claim 8, furthercomprising inhibiting deposition of silicon powder on the ceiling of thereactor above the reaction chambers by positioning a metal or ceramicheat shield plate above the reaction chambers such that reactant gasexiting the reaction chambers is diverted from flowing directly to theceiling of the vessel.
 12. The process as defined by claim 8, furthercomprising:providing the powder catcher in the shape of a cylinder; andinjecting monosilane gas alongside and in a circumferential directionwith respect to the powder catcher.
 13. The process as defined by claim8, further comprising maintaining the relationship ofT2.[.≦.]..Iadd.<.Iaddend.T1.[.≦.]..Iadd.<.Iaddend.T3 where Ti is thewall temperature of the reaction chambers, T2 is the wall temperature ofthe powder catcher, and T3 is the reactor ceiling temperature.
 14. Theprocess as defined by claim 13, further comprising maintaining thetemperature to be T1>25° C., T2<25° C., and T3>70° C.
 15. A process forthe production of polycrystalline silicon rods from a silicon-bearinggas, the process comprising:providing a reactor vessel having aninterior surface including a floor, a wall, and a ceiling, the vesselcontaining (a) .[.a cooled partition with a wall which defines.].multiple reaction chambers, and (b) a powder catcher which comprises acooled wall provided by a heat exchange tube array in the shape of diskthat defines a vertical passageway and which is displaced from andlocated at an elevation above the reaction chambers; positioning astarter filament in each reaction chamber where a polycrystallinesilicon rod is to be grown; heating the starter filaments; passing asilicon-bearing reactant gas through the reaction chambers such thatpolycrystalline silicon deposits on the starter filaments and formssilicon powder due to the thermal decomposition of a silane gas in thereactant gas, the silane gas being selected from the group consisting ofmonosilane, disilane, and mixtures thereof; passing the reactant gas,with entrained silicon powder, from the reaction chambers into the tubearray where the silicon powder deposits the cooled wall; passing thereactant gas from the tube array into the passageway; and recirculatingat least a portion of the reactant gas from the passageway into thereaction chambers. .Iadd.16. The process as defined by claim 1, furthercomprising providing the powder catcher at a location that is not overthe reaction chambers..Iaddend..Iadd.17. The process as defined by claim7, further comprising providing the powder catcher at a location that isnot over the reaction chambers..Iaddend..Iadd.18. The process as definedby claim 8, further comprising providing the powder catcher at alocation that is not over the reaction chambers..Iaddend..Iadd.19. Theprocess as defined by claim 10, further comprising providing the powdercatcher at a location that is not over the reactionchambers..Iaddend..Iadd.20. The process as defined by claim 12, furthercomprising providing the powder catcher at a location that is not overthe reaction chambers..Iaddend..Iadd.21. The process as defined by claim15, further comprising providing the powder catcher at a location thatis not over the reaction chambers..Iaddend.